A process that is commonly used during the manufacture of semiconductor integrated circuit wafers is known as physical vapor deposition (PVD). During a PVD process a metal layer is deposited on an underlying semiconductor wafer by a sputtering process.
Alignment marks on the surface of a semiconductor wafer are typically covered by a shadow tab mask structure in order to prevent the alignment marks from being covered by the metal that is deposited on the wafer during the metal deposition process. A shadow tab mask generally comprises a ring structure that is placed over the circumferential edge of a circular disk of a semiconductor wafer. The shadow tab mask is formed having a number of protrusions that extend from inner edge of the ring structure out over a portion of the surface of the semiconductor wafer when the shadow tab mask is placed over the semiconductor wafer. The location, size and extent of the protrusions (called “tabs”) are such that the tabs cover the alignment marks on the semiconductor wafer when the shadow tab mask is properly aligned with respect to the semiconductor wafer. During a physical vapor deposition (PVD) process the metal that is sputtered over the tabs of the shadow tab mask does not reach the alignment marks that are covered by the tabs. An example of a prior art shadow table mask is described in U.S. Pat. No. 5,456,756.
A physical vapor deposition (PVD) chamber comprises a heater table over which a semiconductor wafer is placed during a PVD process. The heater table is used to heat the semiconductor wafer during the manufacturing process. When the PVD chamber is being prepared for operation a shutter in the form of a disk is temporarily placed over the heater table to protect the heater table from a deposition of Titanium (Ti)/Titanium Nitride (TiN) that is used to condition the PVD chamber.
When the shutter is not being used to shield the heater table from a deposition process, the shutter is kept in a shutter storage receptacle. The shutter is moved from the shutter storage receptacle into place over the heater table by a pneumatic arm. The pneumatic arm also replaces the shutter in the shutter storage receptacle when the shutter is not being used.
FIG. 1 is a block diagram 100 that illustrates a plan view of a prior art shadow tab mask 110. As may been seen in FIG. 1 the shadow tab mask 110 comprises a ring structure having an inner edge 120 and an outer edge 130. In the embodiment shown in FIG. 1 shadow tab mask 110 comprises two tabs 140. Tabs 140 extend inwardly from inner edge 120 so that the tabs 140 will cover alignment marks on a semiconductor wafer (not shown in FIG. 1) when the shadow tab mask 110 is properly aligned with respect to the semiconductor wafer.
FIG. 1 also shows the location of a disk shaped shutter 150 under the shadow tab mask 110. The dotted line 160 represents the outer edge of the shutter 150 under the shadow tab mask 110. The spatial relationship of shutter 150 with respect to shadow tab mask 110 may be more clearly understood by looking at a cross sectional view of shadow table mask 110 and shutter 150 taken along line A-A.
FIG. 2 is a block diagram 200 illustrating the cross sectional view of shadow tab mask 110 and shutter 150 taken along line A-A in FIG. 1. The shutter 150 is placed on the upper surface of heater table 210. Shadow tab mask 110 is placed on top of shutter 150. The two sets of slanted diagonal lines across shutter 150 and heater table 210 indicate that the dimension of the diameter shown in FIG. 2 is not drawn to scale.
FIG. 3 is an enlarged block diagram 300 of an end portion of the cross sectional view of the shadow tab mask 110 and shutter 150 shown in FIG. 2. When the physical vapor deposition (PVD) chamber is conditioned, a layer of Titanium (Ti)/Titanium Nitride (TiN) is deposited over the shadow tab mask 110 and shutter 150. The result of such a deposition process is shown in FIG. 4.
FIG. 4 is a block diagram 400 of the cross sectional view shown in FIG. 3 showing the result of depositing a layer of Titanium (Ti)/Titanium Nitride (TiN) over the shadow tab mask 110 and shutter 150. A deposited layer 410 of Titanium (Ti)/Titanium Nitride (TiN) material covers the exposed portions of the shadow tab mask 110 and a portion of the upper surface of shutter 150. The deposition of the layer 410 creates a fused seam 420 at the juncture of the shadow tab mask 110 and the shutter 150.
When the shadow tab mask 110 is subsequently lifted from the shutter 150, the fused seam 420 of layer 410 will be broken. The breaking of the fused seam 420 causes the explosive release of Titanium (Ti)/Titanium Nitride (TiN) particles throughout the PVD chamber. This causes the particle level to increase throughout the PVD chamber. This is one problem that occurs due to the interaction of shadow tab mask 110 and prior art shutter 150.
Note that because the shadow tab mask 110 is placed on the upper surface of shutter 150, the shadow tab mask 110 is elevated above the shutter 150 so that an undesirable gap 430 is created between the shadow tab mask 110 and the heater table 210. When the Titanium (Ti)/Titanium Nitride (TiN) particles are released throughout the PVD chamber (due to the breaking of the fused seam 420) some of the particles may enter into gap 430.
That is, particles from deposition layer 410 that are free to move throughout the PVD chamber may backscatter into gap 430 between the shadow tab mask 110 and the heater table 210. These particles then cover the surfaces of the inner cavity 440 between shadow tab mask 130 and heater table 210. To achieve better adhesion the surfaces of the inner cavity 440 are not conditioned with a rough texture. Therefore, the Titanium (Ti)/Titanium Nitride (TiN) particles become loosely bonded to the surfaces of the inner cavity 440 and are susceptible to flaking. This is a second problem that occurs due to the interaction of shadow tab mask 110 and prior art shutter 150.
The shadow tab mask 110 rests directly on shutter 150. Consider an embodiment of shadow tab mask 110 in which shadow tab mask 110 has two tabs 140 (as shown in FIG. 1). If the shadow tab mask 110 rests on the two tabs 140 there may be a balancing problem with shadow tab mask 110. This a third problem that may occur due to the interaction of shadow tab mask 110 and prior art shutter 150.
There is therefore a need in the art for a system and method for providing an improved shutter for use with a shadow tab mask and heater table during a conditioning process for a physical vapor deposition (PVD) chamber.